This invention relates generally to the field of injection molding plastic articles, such as blowable plastic parisons, around a set of cylindrical core pins, cooling the articles while on the core pins, and then stripping the molded articles from the core pins for subsequent processing. After the stripping step, but before recycling of the machine to the injection molding station, a problem has existed in detecting parisons or portions of parisons that remain on the core pins.
The art of forming bottles and containers by blow molding has advanced to the stage where several thousands of such articles can be blown each hour. This necessarily requires that the blowable parisons from which the articles are blown be formed rapidly and inexpensively, either by extrusion or injection molding techniques. In injection molding processes, it therefore becomes important to reduce the overall cycle time. A prior injection molding machine disclosed in copending application Ser. No. 738,508, now U.S. Pat. No. 4,136,146, assigned to the assignee of the present invention, has provided the capability of rapid parison formation at low manufacturing cost. A problem exists in the aforementioned injection molding machine, however, in that after the ejection step, parisons or portions of parisons are sometimes left on the core pins. This creates a potentially unsafe and damaging situation if the machine is recycled to the injection mold with any parison residue on the core pins. If parison residue remains on the core pins when the injection mold halves close, the injection mold may be damaged or the next successive parison may be defective.